Passive refrigeration system for the cold chain industry

ABSTRACT

A passive refrigeration box for controlled refrigeration of a product comprising: an outer box including an outer insulation layer; an inner box including an inner insulation layer, and a thermal shield on an outside of the inner insulation layer, the inner box and the outer box defining a vapour channel therebetween; and a thermal link including a thermal layer and a plurality of heat pipes or thermosyphons, the thermal layer and a top section of the inner box defining a coolant chamber, the coolant chamber including a coolant chamber access, and in communication with the vapour channel, and the thermal layer and a bottom section of the inner box defining a load chamber, the load chamber including a load chamber access, each heat pipe or thermosyphon having a condenser section disposed in the coolant chamber and an evaporator section disposed in the load chamber and extending through the thermal layer.

FIELD OF THE INVENTION

The present invention relates to the field of passive refrigerationsystems, for use in refrigerating perishable products during shippingand storage. More specifically, the present invention is directed to arefrigeration system that uses carbon-dioxide-free cooling in the loadchamber, and which has a high degree of temperature regulation. Thesystem may, for example, be used for pallet-sized loads, fortrailer-sized loads and for stationary cold storage facilities, and istherefore scalable.

BACKGROUND

The cold chain industry is responsible for shipping and storingrefrigerated temperature-sensitive products, such as food andpharmaceuticals. Losses can be incurred because of insufficientrefrigeration or improper temperatures. Currently, companies involved inshipping perishable foods must either have expensive electro-mechanicalrefrigeration trucks with multiple refrigerated compartments that can beset to different temperatures, or place all items at a singletemperature and hope the frozen product does not melt and spoil beforedelivery.

U.S. Pat. No. 4,891,954 discloses a refrigeration system (10) consistingof an insulated railcar (12) that utilizes sublimated carbon dioxide(CO₂) to maintain the integrity of stored products. The insulatedrailcar (12) includes a divider (22) that partitions the insulatedrailcar (12) into a lower storage area (26) and an upper bunker (24).The bunker (24) contains a distribution manifold (28) for forming carbondioxide snow and distributing the formed snow throughout the bunker(24). Sublimation ports (30) along each sidewall (18) and end wall (20)allow the sublimated carbon dioxide to pass to the lower storage area(26) to refrigerate the stored products during transit. A plenum (42)and emission vent (44) is provided at each end of the insulated railcar(12) to vent sublimated carbon dioxide to the exterior atmosphere. Theinsulated railcar (12) also includes pressure relief ports (32) locatedsubstantially below the distribution manifold (28) to vent flash gasgenerated during the snow forming process. This technology does notallow for temperature control over time, nor is there a consistenttemperature throughout the chamber. Further, CO₂ is added to the loadchamber.

U.S. Pat. No. 5,460,013 discloses a refrigerated, thin-walled shippingcontainer (8) including a horizontal dividing element (20) forming acompartment (22) for holding CO₂ snow created by passing liquid CO₂through manifold (24) along at least one side of the compartment andspraying the CO₂ snow against the opposite wall. The charging of thecooling compartment generates gas pressure, and the combination designof the charging manifold and pressure release vents allows the operationto be performed without excessive structural damaging pressure buildup.This technology does not allow for temperature control over time, or indifferent regions of the container. Further, gaseous CO₂ is added to thechamber.

U.S. Pat. No. 7,310,967 discloses a cryogenic shipping and storagecontainer, with an on-board cooling unit in the form of a bunker forholding solid refrigerant. The unit can be configured for differentsizes, and is used to refrigerate rather than freeze product. While thissystem allows for better temperature control in the chamber, it requirespower and fans, and therefore is not a passive system. Further, gaseousCO₂ is added to the chamber.

U.S. Pat. No. 8,191,380 discloses a portable active cryo container formaintaining product at refrigerated and/or cryogenic temperatures. Thecontainer comprises a control system to monitor and control the flow ofcooling air from a bunker section to at least one material storagesection wherein temperature sensitive product is contained. The controlsystem is coupled to a fan which enhances heat transfer through forcedconvection when the system moves outside thermal tolerance. The cryocontainer is powered using battery packs or by being plugged into avehicle's 12-volt power supply. While this system allows for bettertemperature control in the chamber, it requires power and fans, andtherefore is not a passive system. Further, gaseous CO₂ is added to thechamber. The coolant, which is liquid nitrogen, travels through a liquidvaporizing heat exchanger. Unlike a heat pipe, it has an open end. Theopen end discharges the coolant into the ambient environment in thechamber.

U.S. Pat. No. 3,714,793 discloses a liquefied gas vaporizer in thebottom portion of the freeze-sensitive product storage chamber withthermal insulation around the liquid vaporizing conduit and thermallyconductive metal floor means contiguously associated with and in heattransfer relation to the thermal insulation. The coolant, which isliquid nitrogen, travels through a liquid vaporizing heat exchanger.Unlike a heat pipe, it has an open end. The open end discharges thecoolant into the ambient environment in the chamber.

U.S. Pat. No. 3,421,336 discloses a system for more uniform distributionof refrigerant in long-haul trailers and railcars by intermittentlyspraying cold fluid into the product chamber and continuously expandingvaporised cold liquid into the same chamber with the production ofexternal work which is recovered to circulate the sprayed cold fluid.

U.S. Pat. No. 7,891,575 discloses a thermal storage and transfer systemthat includes a cooling system and method using ice or other frozenmaterial with heat pipes to produce a cool airstream. Preferably, theice is disposed in a container with the condensers and evaporators ofthe heat pipes respectively inside and outside the container. A fanblows air across the evaporator sections through a duct to circulatewithin an enclosed airspace to be cooled. A separate refrigerationsystem which may be used to independently cool the airspace also freezeswater or another liquid to produce the ice or other frozen material inthe container. The cooling system is broadly applicable, including foruse on motor vehicles to provide cooling for several hours when thevehicle engine is off. A heating system includes an adsorbent heatexchanger for extracting heat from exhaust gases of an engine andheating an enclosed airspace. Again, this is not a passive system, sinceit requires fans.

United States Patent Application Publication No. US2004/0226309discloses a portable, temperature-controlled container for storing andtransporting temperature-sensitive materials. The portable,temperature-controlled container includes a container having a bottomwall, four side walls, and a top wall defining a cargo space. Thecontainer includes a temperature regulating unit connected to thecontainer. The temperature regulating unit comprises a refrigerationunit. The temperature regulating unit is in communication with the cargospace of the container. The container includes a temperature controllerconnected to the container. The temperature controller comprises atemperature control unit and a temperature sensor positioned in thecargo space of the container. The container also includes a powersupply. The temperature regulating unit can include a heating unit.Again, this is not a passive refrigeration system.

U.S. Pat. No. 8,162,542 discloses a cargo container that includes acargo box affixed atop a hollow base, with the base including forklifttunnels extending therethrough with elongate bays disposed parallelthereto. Each bay includes a removable tray for receiving electricalbatteries. And, a temperature control system is disposed on a sidewalladjoining the base. The cargo container has both an electrical heaterand vapor compression refrigeration. Onboard batteries provide powerduring shipping. This is not a passive system.

United States Patent Application Publication No. US2013/0008188discloses a cryogen heat exchanger that includes a container having asidewall defining a chamber in the container for containing a cryogen,and at least one heat exchange assembly having a first portion disposedin the chamber and extending through the sidewall to a second portiondisposed in an atmosphere of a space external to the chamber and at anopposite side of the sidewall for providing heat transfer to theatmosphere. The system uses heat pipes, but also includes at least onefan, and therefore is not a passive system. Temperature can be adjustedby varying the pressure of the cryogen (liquid nitrogen or liquid carbondioxide) in the tank, presumably with a pump or adjusting fan speed.Again, neither of these methods are passive. Other methods of adjustingtemperature do not allow for temperature adjustment on the fly, butrather involve use of a variable volume liquid reservoir to theevaporator section of each heat pipe. The heat pipes are stainless steelor copper.

A refrigerated container that can hold a pallet of product would beuseful for both shipping and storage of perishable products. It would bepreferably if carbon dioxide or other coolant was not added to thestorage compartment (also sometimes referred to herein as the “loadchamber”), either directly or indirectly. Carbon dioxide displacesoxygen and in high concentrations can asphyxiate a person. Dischargingcarbon dioxide vapour directly into the load space compromisestemperature control and because of its very rapid temperature pulldown,compromises the load unit's structural elements. Further, the expansioneffect caused by phase change requires significant volumes of thecryogen vapour to vent the atmosphere, which increases operating costsby increasing the amount cryogen needed. It would be more preferable ifit had a passive heat transfer system with no requirement for forcedconvection. It would be of further advantage if the system allowed fordelivery and storage of cargo at various selected and controlledtemperatures.

SUMMARY OF THE INVENTION

Disclosed herein is a refrigerated system and container for shipping andstorage of perishable products. In one embodiment, the refrigeratedcontainer is sized to hold a pallet of product. Carbon dioxide is notadded or released to the storage compartment, either directly orindirectly. The system has a passive heat transfer system with norequirement for forced convection. The system can be configured to allowfor delivery and storage of cargo at various selected and controlledtemperatures.

In one embodiment, a passive refrigeration box for controlledrefrigeration of a product is provided, the refrigeration boxcomprising: an outer box, the outer box including an outer insulationlayer; an inner box, the inner box including an inner insulation layer,and a thermal shield on an outside of the inner insulation layer, theinner box and the outer box defining a vapour channel therebetween; anda thermal link, the thermal link including a thermal layer and aplurality of heat pipes or thermosyphons, the thermal layer and a topsection of the inner box defining a coolant chamber, the coolant chamberincluding a coolant chamber access, and the coolant chamber incommunication with the vapour channel, and the thermal layer and abottom section of the inner box defining a load chamber, the loadchamber including a load chamber access, each heat pipe or thermosyphonhaving a condenser section disposed in the coolant chamber and anevaporator section disposed in the load chamber and extending throughthe thermal layer.

The passive refrigeration box may further comprise a mesh header belowthe heat pipes or thermosyphons. The passive refrigeration box mayfurther comprise an outer skin on the outer insulation layer and aninner liner on the inner insulation layer. In the passive refrigerationbox, the thermal shield may be an aluminum shield. In the passiverefrigeration box, the coolant chamber access may include an outer lidand an inner lid. In the passive refrigeration box, the inner lid may beseated on a step in the inner box. The passive refrigeration box mayfurther comprise a gasket between the inner lid and the step. In thepassive refrigeration box, the heat pipes may be weld-free heat pipes.

In the passive refrigeration box, the heat pipes may include a workingfluid, the working fluid being one of pentane, propylene, acetone andmethanol. In the passive refrigeration box, the thermal link may be areconfigurable thermal link. The passive refrigeration box may furthercomprise a check valve in the outer lid.

Also disclosed herein, is a passive refrigeration system for thecold-chain industry, the system including a box and a solid coolant, thebox comprising: an outer box, the outer box including an outerinsulation layer; an inner box, the inner box including an innerinsulation layer, and a thermal shield on an outside of the innerinsulation layer, the inner box and the outer box defining a vapourchannel there between; and a thermal link, the thermal link including athermal layer and a plurality of heat pipes or a plurality ofthermosyphons, the thermal layer and a top of the inner box defining acoolant chamber, the coolant chamber including a coolant chamber access,and the coolant chamber in communication with the vapour channel, andthe thermal layer and a bottom of the inner box defining a load chamber,the load chamber including a load chamber access, each heat pipe orthermosyphon having a condenser section disposed in the coolant chamberand an evaporator section disposed in the load chamber and extendingthrough the thermal layer, and the solid coolant is solid carbondioxide.

In the system, the thermal link may be a reconfigurable thermal link. Inthe system, the thermal link comprises a plurality of heat pipes. In thesystem, the heat pipes may be weld-free heat pipes. In the system, theheat pipes may include a working fluid, the working fluid being one ofpentane, propylene, acetone and methanol. In the system, the thermalshield may be an aluminum shield.

Also disclosed herein, is a passive refrigeration box for controlledrefrigeration of a product, the refrigeration box comprising: a bottom,four sides attached to the bottom, an inner lid and an outer lid, thesides including an outer insulation layer and an inner insulation layer,the layers and the inner and outer lids defining a vapour channel therebetween, an aluminum shield adjacent the vapour channel and abutting anouter side of the inner insulation layer and a top of the inner lid, athermal layer, the thermal layer disposed below the inner lid andbetween the inner insulation layers to define a coolant chamber, thecoolant chamber for retaining a coolant, a load chamber, the loadchamber defined by the inner insulation, and the thermal layer, and aplurality of heat pipes or a plurality of thermosyphons, each heat pipeor thermosyphon having a condenser section disposed in the coolantchamber and an evaporator section disposed in the load chamber andextending through the thermal layer.

Also disclosed herein, is a method of refrigerating a load passively,using the refrigeration box described above, the method comprisingloading the load into the load chamber and charging the coolant chamberwith a solid coolant.

The method may further comprise configuring the thermal link to regulatethe temperature of the load. In the method, the solid coolant may besolid carbon dioxide (or “dry ice”).

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described below with referenceto the accompanying drawings in which:

FIG. 1 is a longitudinal sectional view of a heat pipe in accordancewith an aspect of the present invention.

FIG. 2 is a longitudinal sectional view of an end cap and tube end ofthe heat pipe of FIG. 1.

FIG. 3 is a perspective sectional view of the passive refrigeration boxin accordance with an aspect of the present invention.

FIG. 4 is a longitudinal sectional view of passive refrigeration box ofFIG. 3.

FIG. 5 is a longitudinal sectional view an alternative embodiment of apassive refrigeration box.

FIG. 6 is a longitudinal sectional view of an alternative embodiment ofa passive refrigeration box.

FIG. 7A illustrates the operation of a reconfigurable thermal link inaccordance with an aspect of the present invention.

FIG. 7B illustrates the operation of a reconfigurable thermal link inaccordance with an aspect of the present invention.

DESCRIPTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawing(s), which form a part hereof, andwhich show, by way of illustration, exemplary embodiments by which theinvention may be practiced. The invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Thefollowing detailed description is, therefore, not to be taken in alimiting sense.

Except as otherwise expressly provided, the following rules ofinterpretation apply to this specification (written description, claimsand drawings): (a) all words used herein shall be construed to be ofsuch gender or number (singular or plural) as the circumstances require;(b) the singular terms “a”, “an”, and “the”, as used in thespecification and the appended claims include plural references unlessthe context clearly dictates otherwise; (c) the antecedent term “about”applied to a recited range or value denotes an approximation within thedeviation in the range or value known or expected in the art from themeasurements method; (d) the words “herein”, “hereby”, “hereof”,“hereto”, “herein before”, and “hereinafter”, and words of similarimport, refer to this specification in its entirety and not to anyparticular paragraph, claim or other subdivision, unless otherwisespecified; (e) descriptive headings are for convenience only and shallnot control or affect the meaning or construction of any part of thespecification; and (f) “or” and “any” are not exclusive and “include”and “including” are not limiting. Further, the terms “comprising,”“having,” “including,” and “containing” are to be construed asopen-ended terms (i.e., meaning “including, but not limited to,”) unlessotherwise noted.

To the extent necessary to provide descriptive support, the subjectmatter and/or text of the appended claims is incorporated herein byreference in their entirety.

Recitation of ranges of values herein are merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited herein. Where a specific range of values isprovided, it is understood that each intervening value, to the tenth ofthe unit of the lower limit unless the context clearly dictatesotherwise, between the upper and lower limit of that range and any otherstated or intervening value in that stated range, is included therein.All smaller sub ranges are also included. The upper and lower limits ofthese smaller ranges are also included therein, subject to anyspecifically excluded limit in the stated range.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe relevant art. Although any methods and materials similar orequivalent to those described herein can also be used, the acceptablemethods and materials are now described.

Definitions

Heat pipe—in the context of the present invention, a heat pipe consistsof a sealed pipe that un-releasably retains a working fluid. A wick ispresent in the bore of the pipe. (In essence, a heat pipe is aheat-transfer device that combines the principles of both thermalconductivity and phase transition to effectively transfer heat betweentwo solid interfaces. At the hot interface of a heat pipe a liquid incontact with a thermally conductive solid surface turns into a vapor byabsorbing heat from that surface. The vapor then travels along the heatpipe to the cold interface and condenses back into a liquid—releasingthe latent heat. The liquid then returns to the hot interface throughcapillary action (wicking), and the cycle repeats. Due to the very highheat transfer coefficients for boiling and condensation, heat pipes aregenerally highly effective as heat transfer devices.)

Thermosyphon—in the context of the present invention, a thermosyphon issimilar in components and construction to a heat pipe, except itcontains a larger amount of working fluid and it does not contain a wickstructure. It unreleasably retains a working fluid.

Weld-free heat pipe—in the context of the present invention, a weld-freeheat pipe is one that has barbed end caps and barbs on the inside of thetube of the heat pipe proximate the ends. The end caps and tube arepress fit together.

Weld-free, soldered heat pipe—in the context of the present invention, acopper heat pipe is soldered to close the end caps to the tube.

Weld-free, soldered thermosyphon—in the context of the presentinvention, a thermosyphon is soldered to close the end caps to the tube.

Working fluid—in the context of the present invention, a working fluidis one that is present as both a saturated liquid phase and a vapourphase in the heat pipe. The liquid is evaporated to a vapour at theevaporator region of the heat pipe, and the vapour is condensed to aliquid at the condenser region of the heat pipe. For present purposes,any one of pentane, propylene, acetone and methanol, are good candidatesfor use as the working fluid; other refrigerants that are also suitablefor use as the working fluid will be apparent to a person skilled in theart.

Wick—in the context of the present invention, a wick is a material thatlines the bore of the heat pipe and exerts a capillary action on theliquid phase of the working fluid.

Thermal link—in the context of the present invention, a thermal link isan interface for the management of heat flow (thermal energy flow). Thedesign and the material used determine the thermal conduction of thethermal linkage. The thermal linkage includes the heat pipes and aninsulating or conducting layer (the thermal layer).

Reconfigurable thermal link—in the context of the present invention, areconfigurable thermal link refers to a thermal link that can be alteredto change or optimize the thermal conductivity for a given application(temperature requirement).

Solid coolant—in the context of the present invention, charging thecoolant chamber with a solid coolant means that a solid coolant isadded, or a liquid coolant is injected which then changes phase from aliquid to a solid coolant.

DETAILED DESCRIPTION OF THE INVENTION

A heat pipe, generally referred to as 8 is shown in FIG. 1. It is a tube10 that has a first end 12, with a first end cap 14, and a second end16, with a second end cap 18. The second end cap 18 has a fill tube 20extending therefrom. A bore 22 extends from the first end cap 14 to thesecond end cap 18. The fill tube 20 has a crimping end 24 distal to thesecond end cap 18 and a fill tube bore 26. The second end cap 18 has acentral aperture 28. The wall 30 of the central aperture 28 has a step32 upon which the proximal end 32 of the fill tube 20 is seated (as maybe more clearly seen in FIG. 2). A solder bead 34 attaches the fill tube20 to the second end cap 18. In FIG. 1, the crimping end 24 is crimped,after the working fluid has been added to the pipe. A bead of solder 40seals the crimped end 24. The heat pipe 8 has a wick 42 in the bore 22.

As shown in FIG. 2, and using the second end cap as an example, thefirst end 12 and the second end 16 and the end caps 14, 18 are barbed50, with the end cap 14, 18 preferably being the male mating member 52and the ends 12, 16 being the female mating member 54 and also havingbarbs 56. An O-ring 60 is seated in the mating pair. This provides aweld-free heat pipe.

As noted above, the heat pipe or thermosyphon (as the case may be), maybe weld-free and soldered closed.

A passive refrigeration box, generally referred to as 80 is shown inFIG. 3. The refrigeration box 80 provides passive cooling through theuse of heat pipes 8 (for ease of illustration, only a single row of heatpipes is shown in FIG. 3, although it should be understood thatadditional rows of heat pipes or an array of heat pipes would preferablybe used) and with no release of coolant into the load chamber 82. Theouter box 81 includes a bottom 84 attached to four walls 86, and anouter lid 88. The box is preferably constructed to provide sufficientstrength and support for the load and to be moved using a fork lift. Anouter skin 90 of aluminum or steel or plastic is optionally supported bya metal frame 92 in the bottom 84 and four walls 86. A layer of outerinsulation 94 lines the inside 96 of the skin 90 and frame 92. The outerinsulation 94 is preferably closed cell, extruded or expandedpolystyrene or the like and may include vacuum insulated panelinsulation. The bottom 84 includes slots 97 for accepting forks of aforklift.

An inner box 98 includes four inner walls 100, an inner bottom 102, andan inner lid 104. A layer of inner insulation 110 lines the inner liner112 of the walls 100 and the skin 114 of the inner lid 104. The innerinsulation 110 is preferably closed cell, extruded or expandedpolystyrene or the like (including vacuum insulated panel insulation).The inner liner 112 and skin 114 are aluminum or plastic. The innerliner 112 includes stand-offs 116 that extend a short distance into theload chamber 150 to ensure that an air gap is maintained between theinner liner 112 and the load. The outer lid 88 is preferably similarlyconstructed of a skin which is aluminum or plastic, and provided withinsulation that is preferably closed cell, extruded or expandedpolystyrene or the like (including vacuum insulated panel insulation).

Abutting the upper surface 118 of the insulation 110 of the inner lid104 and the outer surface 120 of the inner insulation 100 is a thermalshield 122 which in the preferred embodiment is an aluminum shield 122.The aluminum shield 122 and both the layer of outer insulation 94 on thewalls 86 and the outer lid 88 define a space referred to as vapourchannel 124. The thermal shield 122 helps to manage heat leaks andmaintain the temperature of the cold space. It also decreases the timeto cool a load from its initial higher temperature to steady-state whileconsuming less solid coolant/dry-ice.

As shown in FIG. 4, the inner lid 104 sits on a step 126 in the innerliner 112. A gasket 128 fits between the inner lid 104 and the step 126in the inner liner 112. The vapour channel 124 may be sealed from theambient environment and, optionally, from the coolant chamber 140.Although not expressly shown in FIG. 3, in one embodiment, the vapourchannel 124 can be in communication with the coolant chamber 140, suchthat the vapour channel 124 also serves to circulate the sublimated orevaporated coolant from the coolant chamber 140; in this fashion, thecold sublimated or evaporated (as the case maybe, depending on thecoolant used) vapour of the coolant may also be used to help cool theload chamber. Also optionally, a check valve 125 mounted in the outerlid 88 may be provided, so that a small over pressure can be maintainedinside the vapour channel 124. This prevents the ingress of externalmoist air when the coolant/dry ice charge is depleted. Further, thecheck valve 125 can also serve to prevent the build-up of excess coolant(evaporated or sublimated) in the vapour channel 124. As such, the checkvalve 125 may simply be a one-directional valve, i.e. which allowsvapour to be vented outside to the ambient environment, but prevents airfrom the ambient environment from entering the vapour channel 124. Acoolant 142, which is preferably solid carbon dioxide, is loaded andretained in the coolant chamber 140. Once closed, the coolant chamber140 does not communicate with the ambient environment. The coolantchamber 140 has a plurality of heat pipes 8 extending into the loadchamber 150 through a base 143 of the coolant chamber 140. The base 143and the heat pipes 8 form a reconfigurable thermal link 144. Thereconfigurable thermal link 144 (as described in further detail below)may also allow for customization and optimization of thermal energytransfer between the coolant 142 in the coolant chamber 140 and the loadchamber 150. The coolant chamber 140 is in a top section 146 of theinner box 98. The load chamber 150 is in a bottom section 148 of theinner box 98.

The construction of the heat pipes 8 assist in providing thiscustomization. The portion of the heat pipes 8 extending into thecoolant chamber 140 includes the condenser section 152. Below the base143 and the inner liner 112 is the load chamber 150. The portion of theheat pipes 8 extending into the load chamber 150 includes the evaporatorsection 156. A mesh header 160 protects the heat pipes 8 from damage incase the load in the load chamber 150 shifts. The mesh may be made fromaluminum, steel or plastic and additionally functions to ensuresufficient space for air circulation. The mesh header 160 extends acrossthe load chamber 150 in the vicinity of the top 162 of the load chamber150. The load chamber 150 is an enclosed space.

An inner door 170 and an outer door 172 may be constructed in the samemanner and with the same materials as the lids 88, 104. These doors donot impede the vapour channel 124. At least one temperature sensor 176may be located in the load chamber 150 and is in electroniccommunication with a display 178 that is remote to the refrigerator box80 or is on an outer surface 178 of the refrigerator box 80.

In one embodiment, the refrigeration box 80 is sized to accept a palletload of product. The load is placed in the refrigeration box and thenthe refrigeration box can be moved into and out of a storage facility ora truck for transport. Different refrigeration boxes operating atdifferent temperatures can be placed side by side and can be deliveredtogether or independently of other refrigeration boxes in the truck.This increases the flexibility in the truck load to be delivered, allowsfor optimization of storage conditions for product, and reduces energyconsumption and the associated pollution caused by running a generatorto cool a truck load.

In an alternative embodiment, a side access allows the coolant chamber140 either to be slid out and charged/recharged with solid coolant 142,or simply accessed on the side and charged.

In another embodiment, shown in FIG. 5, the passive refrigeration box 80of FIGS. 3 and 4 further includes a liquid injection port 180 and adistribution manifold 182 in the coolant chamber 140 for the addition ofliquid carbon dioxide. This liquid carbon dioxide flashes into solidcarbon dioxide snow (solid coolant 142), hence charging the coolantchamber with solid coolant 142. In an embodiment, such a charging supplyof liquid carbon dioxide may be provided/stored with the passiverefrigeration box 80 for ready convenience.

In another embodiment, shown in FIG. 6, the refrigeration box is sizedto fit as a single unit in an ISO container 200, hence it is slightlysmaller than the inside dimensions of an ISO container 200. The loadchamber 150 has a load chamber access 202 that may comprise an innerdoor 204 and an outer door 206. The coolant chamber access 208 may bethrough lids or an access 208 on the side, as shown in FIG. 6. Theconstruction and relationship between the doors is the same as thelids—there is a thermal shield 206 on the outer side 208 of the innerdoor 202 and the vapour channel 210 has an unimpeded path between thedoors 202, 204.

In another embodiment, the refrigeration box is a container fortransport on a trailer or a flat bed. It again may be configured withdoors and is as described and shown in FIG. 6.

In another embodiment, the refrigeration box 80 is a trailer. It againmay be configured with doors and is as described and shown in FIG. 6.

In yet another embodiment, the heat pipes in the refrigeration box orsystem are replaced with thermosyphons.

One embodiment of a reconfigurable thermal link (mentioned above as 144)is illustrated in FIGS. 7A and 7B (and generally referenced therein as249). The function of the reconfigurable thermal link 249 is to modulatethe thermal resistance along a specific thermal conductive pathwayjoining a relatively warm region to a relatively cooler region. Byphysically adjusting the internal element(s) of the reconfigurablethermal link, the thermal resistance of the aforementioned thermallyconductive path can be altered to affect a change in the rate at whichheat energy is transferred from the relatively warm region to therelatively cooler region.

When the reconfigurable thermal link 249 is placed in the thermal pathbetween the load chamber 150 (relatively warm region) and the coolantchamber 140 (relatively cooler region), the rate of heat transfer may bemodulated to the point that some degree of load chamber temperaturecontrol can be achieved. In one embodiment, the reconfigurable thermallink 249 can be placed at the condenser end of the heat pipes orthermosyphon arrangement (relatively warm region) and the far coldercoolant chamber 140, to affect control over the heat transfer rateachieved between the relatively warmer region and the relatively coolerregion.

FIG. 7A shows a relatively warmer region 250, a relatively cooler region251 and a heat transfer path 252. The reconfigurable thermal link ismade up of a thermally conductive housing 253 that is divided into twoparts by a thermally insulating housing barrier 254. Together thethermally conductive housing elements 253 and the thermally insulatinghousing barrier 254, make up the entire housing 258. Inside the housing258 there is a cavity 255 that is partially occupied by a moving element259. A portion of the moving element 259 is made up of a thermallyconductive end 256 and a thermally insulating end 257. The movingelement 259 is capable of be moved the entire width of the internalcavity 255.

FIG. 7A shows the moving element 259 in an internal position whereby thethermally resistive path from the relatively warm location 250 to therelatively cooler location 251 is minimized. Heat travels through thethermally conductive housing 253, through the thermally conductiveportion of the internal moving element 256, through the thermallyconductive housing 253 and finally out to the relatively cooler regionbeyond 251. At each stage of this thermal path, heat is allowed totravel through thermally conductive materials, thus making the totalthermal resistance of this path low.

FIG. 7B shows a perspective view of the reconfigurable thermal link 249with the internal moving element 259 shifted in such a way as to producea large thermal resistance impeding heat transfer from relatively warmlocation 250 to relatively cooler location 251. In this configuration,the pathway for heat to transfer is substantially blocked by the dualinsulating materials present in the internal moving element 257 and thehousing insulated segment 254. The thermal resistance of both potentialheat transfer pathways is very high as a result of the thermalinsulating materials that now occupy the potential heat transfer path(s)252.

The movable internal thermal element 259 can be motivated to changeposition by a number of means. Some of these means are passive in thatthey use no electrical energy to operate, while other motivatingmechanisms may use non-passive methods.

While example embodiments have been described in connection with what ispresently considered to be an example of a possible most practicaland/or suitable embodiment, it is to be understood that the descriptionsare not to be limited to the disclosed embodiments, but on the contrary,is intended to cover various modifications and equivalent arrangementsincluded within the spirit and scope of the example embodiment. Thoseskilled in the art will recognize, or be able to ascertain using no morethan routine experimentation, many equivalents to the specific exampleembodiments specifically described herein. Such equivalents are intendedto be encompassed in the scope of the claims, if appended hereto orsubsequently filed.

1. A passive refrigeration box for controlled refrigeration of aproduct, the refrigeration box comprising: an outer box, the outer boxincluding an outer insulation layer; an inner box, the inner boxincluding an inner insulation layer, and a thermal shield on an outsideof the inner insulation layer, the inner box and the outer box defininga vapour channel therebetween; and a thermal link, the thermal linkincluding a thermal layer and a plurality of heat pipes or a pluralityof thermosyphons, the thermal layer and a top section of the inner boxdefining a coolant chamber, the coolant chamber including a coolantchamber access, and the coolant chamber in communication with the vapourchannel, and the thermal layer and a bottom section of the inner boxdefining a load chamber, the load chamber including a load chamberaccess, each heat pipe or thermosyphon having a condenser sectiondisposed in the coolant chamber and an evaporator section disposed inthe load chamber and extending through the thermal layer.
 2. The passiverefrigeration box of claim 1, further comprising a mesh header below theplurality of heat pipes or the plurality of thermosyphons.
 3. Thepassive refrigeration box of claim 1, further comprising an outer skinon the outer insulation and an inner liner on the inner insulation. 4.The passive refrigeration system of claim 1, wherein the thermal linkincludes the plurality of heat pipes.
 5. The passive refrigeration boxof claim 1, wherein the thermal shield is an aluminum shield.
 6. Thepassive refrigeration box of claim 1, wherein the coolant chamber accessincludes an outer lid and an inner lid.
 7. The passive refrigeration boxof claim 6, wherein the inner lid is seated on a step in the inner box.8. The passive refrigeration box of claim 1, further comprising a gasketbetween an inner lid and a step in the inner box.
 9. The passiverefrigeration box of claim 1, wherein the plurality of heat pipes areweld-free heat pipes.
 10. The passive refrigeration box of claim 9,wherein the plurality of heat pipes include a working fluid, the workingfluid selected from a group consisting of acetone, methanol, pentane,and propylene.
 11. The passive refrigeration box of claim 1, wherein thethermal link is a reconfigurable thermal link.
 12. The passiverefrigeration box of claim 6, further comprising a check valve in theouter lid, wherein the check valve is in communication with the vapourchannel.
 13. A passive refrigeration system for the cold-chain industry,the system including: a box and a solid coolant, the box comprising: anouter box, the outer box including an outer insulation layer, an innerbox, the inner box including an inner insulation layer, and a thermalshield on an outside of the inner insulation layer, the inner box andthe outer box defining a vapour channel therebetween; and a thermallink, the thermal link including a thermal layer and a plurality of heatpipes or a plurality of thermosyphons, the thermal layer and a top ofthe inner box defining a coolant chamber, the coolant chamber includinga coolant chamber access, and the coolant chamber in communication withthe vapour channel, and the thermal layer and a bottom of the inner boxdefining a load chamber, the load chamber including a load chamberaccess, each heat pipe of the plurality of heat pipes or thermosyphon ofthe plurality of thermosyphons having a condenser section disposed inthe coolant chamber and an evaporator section disposed in the loadchamber and extending through the thermal layer, and where the solidcoolant is solid carbon dioxide.
 14. The system of claim 13, wherein thethermal link is a reconfigurable thermal link.
 15. The system of claim13, wherein the thermal link includes the plurality of heat pipes. 16.The system of claim 13, wherein the heat pipes are weld-free heat pipes.17. The system of claim 16, wherein the heat pipes include a workingfluid, the working fluid selected from a group consisting of acetone,methanol, pentane, and propylene.
 18. The system of claim 13, whereinthe thermal shield is an aluminum shield.
 19. A passive refrigerationbox for controlled refrigeration of a product, the refrigeration boxcomprising: a bottom; four sides attached to the bottom; an inner lid;and an outer lid, the sides including an outer insulation layer and aninner insulation layer, the layers and the inner and outer lids defininga vapour channel therebetween, an aluminum shield adjacent the vapourchannel and abutting an outer side of the inner insulation layer and atop of the inner lid; a thermal layer, the thermal layer disposed belowthe inner lid and between the inner insulation layers to define acoolant chamber, the coolant chamber for retaining a coolant and incommunication with the vapour channel; and a load chamber, the loadchamber defined by the inner insulation layer and the thermal layer; anda plurality of heat pipes, each heat pipe of the plurality of heat pipeshaving a condenser section disposed in the coolant chamber and anevaporator section disposed in the load chamber and extending throughthe thermal layer.
 20. A method of refrigerating a load passively, usingthe refrigeration box of claim 1, the method comprising loading the loadinto the load chamber and charging the coolant chamber with a solidcoolant.
 21. The method of claim 20, further comprising configuring thethermal link to regulate the temperature of the load.
 22. The method ofclaim 20, wherein the solid coolant is solid carbon dioxide.